Season beef with salt and pepper. Heat a large skillet over medium-high. Add 1 tablespoon oil and half of beef, in a single layer; cook, turning a few times, until browned all over, 5 to 7 minutes. Transfer to a 5-to-6-quart slow cooker. Repeat with remaining oil and beef. Add shallots and wine to skillet; cook, scraping up browned bits, until wine has almost evaporated, about 3 minutes. Transfer to slow cooker; stir in tomatoes with their juices, fennel, rosemary, and zest. Cover and cook on high until meat is fork-tender, about 4 1/2 hours.
Stir in olives; season with salt and pepper. Remove rosemary; serve, with mashed potatoes, orange wedges, and more pepper.